I. Field
The following description relates generally to communications systems, and more particularly to power conservation components that facilitate efficient sleep mode operations in an access terminal.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data may be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources. For instance, a system may use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing, (OFDM), and others.
Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-user version of the popular OFDM digital modulation scheme. Multiple access is achieved in OFDMA systems by assigning subsets of sub-carriers to individual users. This allows concurrent low data rate transmission from several users. Based on feedback information regarding channel conditions, adaptive user-to-sub-carrier assignment can be achieved. If the assignment is performed sufficiently fast, this further improves the OFDM robustness to fast fading and narrow-band co-channel interference, and allows it to achieve even better system spectral efficiency.
A different number of sub-carriers can be assigned to different users, in view to support differentiated Quality of Service (QoS) i.e., to control the data rate and error probability individually for each user. Thus, OFDMA resembles code division multiple access (CDMA) spread spectrum, where users can achieve different data rates by assigning a different code spreading factor or a different number of spreading codes to each user.
OFDMA can also be seen as an alternative to combining OFDM with time division multiple access (TDMA) or time-domain statistical multiplexing i.e., packet mode communication. Low data rate users can send continuously with low transmission power instead of using a “pulsed” high-power carrier. Constant delay, and shorter delay, can also be achieved. However, OFDMA can also be described as a combination of frequency domain and time domain multiple access, where resources are partitioned in the time-frequency space, and slots are assigned along an OFDM symbol index as well as OFDM sub-carrier index.
In addition to the wireless access techniques such as OFDMA, common wireless communication systems employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or uni-cast services, where a data stream may be a stream of data that can be of independent reception interest to a mobile device. A mobile device within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, a mobile device can transmit data to the base station or another mobile device.
Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations.
One always present issue for the mobile devices is the ability to conserve power. Such devices generally operate on battery power and the ability to conserve power provides great utility for users of the devices. With respect to OFDMA devices, these often operate in bursts referred to as sleep mode operation where power is conserved and wake-up operation where the device communicates with a respective base station. Thus, by minimizing wake-up time, power can be conserved and battery life can be increased.